Heat exchanger



FIG. 1 is a front, bottom, left-side perspective view of a heatexchanger comprising a new, original and ornamental design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a left-side view thereof;

FIG. 6 is a right-side view thereof;

FIG. 7 is a bottom, front, left-side perspective view of the heatexchanger in accordance with a second embodiment;

FIG. 8 is a front view thereof;

FIG. 9 is a bottom view thereof;

FIG. 10 is a top view thereof;

FIG. 11 is a left-side view thereof; and,

FIG. 12 is a right-side view thereof.

CLAIM The ornamental design for a heat exchanger, substantially asshown.